The invention relates to image processing, and more particularly to image filtering methods and related devices such as digital and video cameras.
There has been considerable growth in the sale and use of digital cameras, both still and video, in recent years. FIG. 4 is a block diagram of a typical digital still camera which includes various image processing components, collectively referred to as an image pipeline. Color filter array (CFA) interpolation, gamma correction, white balancing, color space conversion, and JPEG (or MPEG for video) compression-decompression constitute some of the key image pipeline processes. The typical color CCD consists of a rectangular array of photosites (pixels) with each photosite covered by a color filter: e.g., red, green, or blue. Thus to recover a full-color image (all three colors at each pixel), a method is required to calculate or interpolate values of the missing colors at a pixel from the colors of its neighboring pixels. Such methods lead to artifacts in the full color image which should be removed by filtering.
Similarly, high-frequency elements of video images are commonly eliminated using conventional linear filters. However, the size of such filters becomes large when the desired characteristics are demanding, and this results in prohibitively large circuit size.
Infinite impulse response (IIR) filtering is often used in acoustical signal processing. However, it is little used in image processing due to its side effects, which are often imperceptible in sound but apparent in images.
Filtering using the matching method compares input signals with a stored database and outputs appropriate signals. Although this method works well in some situations, the output quality can be low if the database does not match the input. Also, this method consumes large amounts of memory and computational power.